The present invention relates to rheometer instruments and similar apparatus for measuring visco-elastic properties of fluent materials (e.g. viscometers), such as liquids, gels, slurries, powder masses, plastics, elastomers, clays, foodstuffs and the like, and more particularly to enabling a new paradigm of the field of achieving low friction and high sensitivity without a complex or expensive apparatus arrangement. The sensing shaft control sub-assembly of the invention is also useful for shaft elements of other kinds including, e.g. probes, rotors or float parts, delicate medical and scientific instruments.
Rheometers measure flows of fluent materials (liquids, slurries, suspensions, elastomers, plastics, gels, melts, (powdery masses), plastics, elastomers, clays, foodstuffs and the like where adequate characterization demands more than a viscosity measurement that can be made by a viscometer. The field of rheometers includes instruments using well known per se rotational cylinders and cone-plate devices contacting the materials to be measured and other forms (e.g. extrusional and capillary forms).
State of the art is summarized and advanced in U.S. Pat. No. 7,207,210 of D. J. Moonay and U.S. Pat. Nos. 5,167,143 and 4,175,425 (all of common assignment with the present application) and references cited therein, all incorporated herein by reference as though set out at length herein.